To determine electrical changes in the heart in a chronic, nonstatus model of epilepsy. Electrocorticography (ECoG) and electrocardiography (ECG) of nine animals (five made epileptic by intrahippocampal injection of tetanus neurotoxin (TeNT) and four controls), are monitored continuously by radiotelemetry for up to 7weeks. Epileptic animals develop a median of 168 seizures, with postictal tachycardias reaching a mean of 487 beats/min and lasting a mean of 661seconds. Ictal changes in heart rate include tachycardia and in the case of convulsive seizures, bradyarrhythmias resembling Mobitz type 1second-degree atrioventricular block; notably the P-R interval increased before block. Postictally, the amplitude of T wave increases. Interictally, QT dependence on RR is modest and conventional QT corrections prove ineffective. Interictal QT intervals, measured at a heart rate of 400bpm, increased from 65 to 75ms, an increase dependent on seizure incidence over the preceding 10-14days. Repeated seizures induce a sustained tachycardia and increase in QT interval of the ECG and evoke arrhythmias including periods of atrioventricular block during Racine type 4 and 5 seizures. These changes in cardiac function may predispose to development in fatal arrhythmias and sudden death in humans with epilepsy. Wiley Periodicals, Inc. 2020 International League Against Epilepsy.